MATLAB: sct_seg.m: added todo, minor modifs on doc
MATLAB: sct_seg.m: added todo, minor modifs on doc

Former-commit-id: fdaf59259e542eaf36fd592e65065328d691af3b
Former-commit-id: 9f6b1c685d874c36e7649d324d1e71a665eb29a4
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox